Translations are horribly bad! Is there a way to improve them?

When using the built-in translation functionality I get horribly bad results for my use case (translate to German). So bad in fact that some texts become nearly unreadable gibberish. It feels like how machine translations were 20 years ago.

I know that Firefox’s translation system works with offline data only and locally on my machine, and thus is very, very, very limited compared to specialized systems like DeepL – and even the common LLMs.

But I wonder: Is there a way to improve the system? Can I feed it more data to make it better? Can I do more than just download the translations in the settings?

I know I can always use extensions for sending pages or text to the common online translation services, but since Firefox has that built-in I’d love to use it – but it needs to return better results.

Any ideas are welcome!

Thank you and vielen Dank :)